1. Field of the Invention
The present invention is directed to an improved manufacturing process for extruding or molding hollow thermoplastic bodies according to which the substance to be molded is thermally conditioned by cooling in a controlled and homogenous manner before being placed in a calibration die. The invention also pertains to objects prepared by this process.
2. Description of the Prior Art
In the classic prior art process the substance to be molded is melted and then continuously forced by a feeding device through an aperture of the appropriate form. The melted mass is then brought in contact with a conformator or mold in which it is deformed and progressively solidified in such a manner that it retains the form permanently.
Such processes require polymers having consistencies when molten which are sufficient to keep the polymer from being deformed under its own weight during the phase when the melted mass emerges from the die, before entering the conformator or the mold. Without such consistency, irregularities in the thickness of the wall of the finished object or weak points resulting in breakage of the extrusion products may occur, thereby completely disrupting the course of the process.
To avoid these inconveniences, it has been proposed to employ total guidance devices such as that described in the French Pat. No. 1,114,680, wherein a linkage or cylindrical coupler made of a poor heat conducting substance is inserted between the feeding pump and the molding device making it possible to lower the temperature to the maximum extent at the point where the melted substance enters the molding device. More recently, in French Pat. No. 2,132,141, a process for extruding crystalline textured profiles made of saturated polyesters has been disclosed wherein the substance to be molded is forced into an intermediate heated calibration die, which is thermally insulated from the head of the extruding machine, prior to introduction into the main die.
Unfortunately, the processes heretofore known in the art are not adapted to the production of tubes and profiles from thermoplastics having low consistencies. The handling of such thermoplastics requires slow cooling which results in low product output and often results in the formation of crystalline polymers. The only means of molding low consistency thermoplastics, heretofore recognized, is by injection molding, or blow molding or other types of molding by transfer. Thus, there remains a need in the art for a continuous extrusion and molding process which is particularly adapted for molding low consistency thermoplastic polymers.